Moisture Drydown in Ultra-High-Purity Oxygen Systems

Semiconductor manufacturing fabs use ultra-high-purity (UHP) oxygen for various process applications such as oxide growth, plasma etch, and chemical vapor deposition. Moisture is identified as one of the key impurities that can affect device production. Moisture drydown in inert gas delivery systems was studied extensively. However, moisture drydown or outgassing characteristics in oxygen were found to be different from those of inert gas systems. Moisture adsorption and desorption in UHP oxygen systems were studied using advanced APIMS techniques for trace-level moisture analysis. To understand moisture reaction pathways, isotopic water was used as an adsorbate on 316L electropolished stainless steel (EPSS) surfaces. Experimental results from moisture drydown in the EPSS tubing were used to validate a theoretical model developed to predict the moisture drydown performance of large-scale, oxygen distribution systems. Both experimental and model results were shown to be useful in UHP oxygen system design, cost control, metrology, and contamination control.